1. Field of the Invention
The present invention relates to an endoscope, and more particularly relates to an endoscope of the type having in its imaging system a solid state imaging system in its viewing head which accepts visual image information of a scene contained in an object to be observed and converts it to an electrical, output data signal for presenting a picture on the screen of viewing equipment.
2. Description of the Prior Art
As well known in the art, an endoscope generally used is made up of an image transmission optical fiber bundle with its end faces being faced to an objective or image forming lens and an eyepiece, respectively. The objective is arranged to focus a visual image of the scene inside the interested object such as a living body on the end face of the image transmission optical fiber bundle. The visual image thus focused is transmitted to the opposite end face of the optical fiber bundle so as to be observed through the eyepiece. Specifically, as shown in FIG. 1, the conventional endoscope, namely a fiberoptic endoscope, comprises a control section 10, a flexible section 12 connected to the control section 10 insertable into a cavity or opening of a living body to be ovserved and a connection section 16 extending from the control section 10 to be connected to a control unit 14 including an illumination light source and various control equipment therein.
In such fiberoptic endoscope of the type having the optical fiber bundle for visual image transmission from one end to the opposite end gace thereof, the control section 10, as shown in FIG. 2, necessarily comprises a grip section 10A which allows one-hand grasping and an eyepiece section 17 including an eyepiece lens or lenses therein which is disposed on the uppermost face of the control section 10. Provided on the front face of the control section 10 are first and second manually operable buttons 18 and 20 for air and water supply control and suction control, respectively.
When using the fiberoptic endoscope mentioned above for observation, an operator is required to firmly grasp the grip 10A of the control section 10 with the middle, medicinal and little fingers 22A, 22B, 22C of his left hand and to operate the first and second buttons 18, 20 with his forefinger 22D, while looking at a magnified image through the eyepiece lens 17. To look through the eyepiece section 17, the operator is required to bring the control section 10 close to his face by raising his arm, or to bring his head close to the eyepiece section 17 by bending his body forward. Therefore, the operator is obliged to assume an unnatural posture, resulting in his arm, waist and the like becoming numb.
Recently, a video endoscope has been proposed which has in its imaging system a solid state imaging device, such as a charge coupled device (CCD) and an image sensor of metal oxide silicon (MOS) type, which is carried in a viewing head thereof adapted for insertion into a cavity. The solid state imaging device accepts visual image information of a scene contained in an object to be observed and converts it to an electrical output data signal or a video signal for presenting a picture on a screen of viewing equipment such as a television set. Because the video endoscope employing a solid state imaging device, different from the conventional fiberoptic endoscope of the type having an image tranmission optical fiber bundle in its imaging system, presents a visual image on a screen, it has the advantage of requiring no eyepiece section and of no restriction in the shape of the control section. Since control section is not restricted in its shape, an operator can easily handle the instrument in a comfortable posture while seeing the picture on the screen.
In this type of video endoscope, there is a serious problem in that the characteristics of the solid state imaging devices vary widely. The solid state imaging devices of different characteristics result in discrepancies between full color images which appear on a screen monochromatic images of different luminance levels. In order to solve the problem, it has been necessary to adjust levels of driving signals for solid state imaging devices corresponding to their characteristics, respectively. For this reason heretofore a level adjusting device has been provided in the control unit which is to adjust the level of the driving signal corresponding to the characteristics of the solid state imaging device incorporated in the video endoscope prepareted. Alternatively, it is required to provide one control unit every video endoscope for the purpose of the elimination of complicated operation. However, the provision of the level adjusting device in the control unit is incidentally accompanied by an additional operation every time changing video endoscopes, and the provision of individual control units arises the problem of a large place for putting them and a high cost of installation.